Researches On Pattern Reconfigurable Antenna Applied In Wireless Communications

With the rapid development of wireless communications, people have more pressing needs on the high-speed, high-capacity communication systems, but the growing scarcity of the spectrum resource restricts the enhancements of the communication capacity and data transmission rate. Currently, the widely used dual-polarized antenna is capable of providing polarization diversity and polarization reuse, which can effectively enhance the capacity of the channel and reduce the influence of multi-path interference. For the pattern reconfigurable antenna, it can effectively reduce the interference and increase the signal coverage by redirecting the main beams. Combined with the advantages of these two kinds of antennas, dual-polarized pattern reconfigurable antenna can be designed to greatly reduce the noise interference and improve the quality of communications. For this purpose, two ±45° dual- polarized pattern reconfigurable antennas have been designed in this thesis.The main contents of the thesis are as follows:The first chapter mainly introduces the research situation of the dual-polarized antennas, pattern reconfigurable antennas and multiple-parameter reconfigurable antennas, and indicates the purpose of conduct research on dual-polarization pattern reconfigurable antennas.The second chapter describes some basic theories of antennas, which is applied to the antenna designs in this thesis, including microstrip antenna theory and Yagi-Uda antenna theory.The third chapter presents the design and improvement of a ±45° dual-polarized pattern reconfigurable dipole antenna. The antenna consists of two orthogonal dipoles, with parasitic elements. By controlling the switches on the parasitic elements, dual-polarization and pattern reconfiguration can be achieved. The antenna is a full planar structure and has the advantages of simple structure, low cost and easy fabrication. Each polarization of the antenna can realize four different radiation pattern modes, among which there are two patterns with their maximum gain directions titled to ±27°, with gains higher than 9 dBi.In Chapter four, a dual-polarized pattern reconfigurable microstrip antenna loaded with varactors is designed. The antenna contains a driven patch and two parasitic patches, with varactors installed over the annual slot etched on each parasitic patch. The parasitic patch can act as a director or a reflector by controlling the capacitance value of the varactors, thus four radiation pattern modes can be realized. The patterns of the two ports agree well with each other in all the four modes. In order to increase the deflection angles of the beams, without increasing the antenna size, two parasitic elements are loaded on both sides of the excitation patch, the maximum gains direct to ±40 degrees. The proposed antenna is fabricated and measured, and the measured results have reasonable agreement with the simulation results. Although there are still some discrepancies, the reasons of discrepancies are analyzed.In the last chapter, a summarization for the research work is made and the deficiencies of the work and the follow-up work are put forward.